The present invention relates generally to flexible fluid-tight seals for pipe joints, and more particularly to a novel and improved gasket particularly suited for sealing bell and spigot joints of round concrete sewer and culvert pipes.
Pipe joints, particularly those encountered in concrete sewer and culvert pipes are fabricated in many configurations and sizes to meet specific requirements and users' preferences, the most common being the bell-and-spigot joint. Sufficient clearance is provided at the joint for a sealant such as an O-ring gasket, caulking or the like depending upon the nature and pressure of the fluid being conveyed. Some sealants are integrally installed at the factory during fabrication of the pipes, while others are simply applied at the job site. For very large diameter concrete pipes, such as in storm and sanitary sewer systems, field installation of the gaskets is frequently preferred.
The O-ring gasket is used, but with limited success, particularly with respect to large diameter pipe joints. The O-ring is typically mounted on the spigot, and the spigot is then pushed into the bell causing the O-ring to roll further onto the spigot until it reaches roughly the center of the pipe connection. Dirty or uneven surfaces, poor or improperly applied lubricants, misaligned pipes, and excessive force may cause the O-ring to distort non-uniformly resulting in weak seals or even total gaps. Some pipe spigots include a circumferential groove or a single- or double- offset shoulder to keep the O-ring from rolling as the pipes are interconnected. However, the diameter of the O-ring in radial cross section is usually greater than the depth of the groove or shoulder and the ring may still roll over the inside edge of the groove, become snagged or shear off segments of the O-ring as the spigot enters the bell.
Various gasket configurations have been used or suggested for overcoming these deficiencies. For example, U.S. Pat. No. 4,565,381 to Joelson discloses a rib-type angular gasket suitable for grooved or offset concrete pipe spigots. For providing self-alignment, the gasket includes a base with inner, intermediate and outer sealing ribs of incrementally increased outside diameter. U.S. Pat. No. 2,271,777 to Nathan and U.S. Pat. No. 2,882,073 to James show similar rib-type gasket configurations for bell-and-spigot pipe joints. In each of these gaskets, it is essential that they be placed on the spigot with the inner or smallest diameter rib closest to the end of the spigot. The ribs of the Nathan and James gaskets are also slightly inclined outwardly to prevent the pipes from separating.
The elasticity of the rib-type gasket also serves conflicting or cross-purposes. For example, high fluid pressure conditions require a relatively hard rubber in order for the ribs to maintain a tight seal, but the hardness makes th gasket difficult to stretch onto a spigot. Consequently a softer rubber gasket would be preferred because it is easier to install, but the ribs may be too soft to withstand high pressure conditions.